The present invention relates to a pneumatic tire, more particularly to an improved bead structure being capable of improving durability of the bead portion.
In general, a pneumatic tire is provided with a carcass comprising one ply of cords turned up around a bead core in each bead portion from the axially inside to the axially outside of the tire. The turned up portion (d) is, as shown in FIG. 6A, extended radially outwards beyond the radially outer end of the bead core (b) and terminates in the lower sidewall portion. In such a structure, at the carcass ply edge or the radially outer end (de) of the turned up portion (d), a stress concentration is liable to occur during running because the deformation of the lower sidewall portion is relatively large. If the deformation is extremely large, a separation failure starting from the carcass ply edge (de) tends to be caused.
In the laid-open Japanese patent application JP-A-11-321244, in order to avoid such stress concentration on the carcass ply edge (de), the carcass ply edge portion (d) is wound once around the bead core (b) to terminate in the bead portion, abutting on the radially outer surface (ba) of the bead core (b), as shown in FIG. 6B.
Such construction, however, tends to become insufficient for securing the carcass ply edge to the bead core under extremely severe service conditions, for example, high speed running under a heavy load and high inner pressure. And there is a possibility that the carcass ply slips from the bead core.
It is therefore, an object of the present invention to provide a pneumatic tire in which, even under extremely severe service conditions, the carcass ply edge is secured safely to the bead cores to improve the durability of the bead portion.
According to the present invention, a pneumatic tire comprises
a pair of bead portions each with a bead core therein,
a carcass comprising one ply of cords extending between the bead portions through a tread portion and sidewall portions and turned back in each bead portion from the axially inside to the axially outside of the tire and wound around the bead core in each bead portion so as to form a pair of wound portions and a main portion therebetween,
each wound portion having a radially outer part extending axially inwards along the radially outer face of the bead core to have a length not less than 0.5 times the width of said radially outer face when measured along the radially outer face,
each bead portion provided between the radially outer part and the radially outer face of the bead core with an organic fiber cord layer,
a distance between the carcass cords in the radially outer part and the radially outer face of the bead core being in a range of from 0.05 to 1.0 times the section height of the bead core when measured in a normal direction to the radially outer face of the bead core.